Members of the Parvoviridae family of viruses are common animal and insect pathogens, which are further classified into the subfamily Parvoviridae based at least on the ability to infect vertebrate cells. Parvovirinae belonging to the genus Erythrovirus are known to infect humans and include, for example, the prototypical parvovirus B19 referred to as Au (genotype 1) as well as variants such as A6 (genotype 2), and V9 and D91.1 (genotype 3). They are non-enveloped viruses that comprise a single-stranded, linear DNA genome. For example, the prototypical human erythrovirus known as parvovirus B19-Au (See e.g., GenBank Accession Number: M13178) has a linear DNA genome of approximately 5.6 kilobases in length.
Discovered in 1975, parvovirus B19 was subsequently linked to an aplastic crisis in a patient with sickle-cell disease. The virus has since been shown to cause or be associated with a variety of conditions and diseases including erythma infectiosum (EI) (fifth disease of childhood), spontaneous abortion, and certain forms of acute arthritis.
Erythrovirus are ubiquitous and contagious. In the case of parvovirus B19, an estimated 60% of adults are seropositive. Children are particularly susceptible at the age when they begin to play together regularly and attend school, the peak season for infection being in the spring and early summer.
In addition to transmission through airborne infections and close contact, human erythrovirus can also be transmitted vertically from a pregnant woman to her fetus. For example, among pregnant women with active cases, about 30% of the fetuses will become infected with parvovirus B19. And, it is now well documented that parvovirus B19 can cause spontaneous abortion when infection occurs within the first six weeks after conception. Infection at this early stage causes massive abnormalities that are inconsistent with life.
Transmission of human erythrovirus also can occur via blood or plasma products of various kinds. For example, cases of symptomatic illness have been reported to be due to blood products prepared from parvovirus B19-containing plasma pools. Parvovirus B19 DNA has been detected in single donations, in plasma pools, and in plasma derivatives (e.g., clotting factors, albumin, antithrombin III, and immunoglobulins) produced by different processes. Parvovirus B19 transmission has also been found in patients treated with clotting factors, as shown by a higher seroprevalence in treated hemophiliacs, by the presence of parvovirus B19 DNA, and by active seroconversion. Unfortunately, the risk of human erythrovirus transmission by blood/plasma products is enhanced by the virus's resistance to effective inactivation methods such as heat and solvent-detergent treatments.
Therefore, health risks from exposure to human erythrovirus continue to exist, and identification and characterization of variants of the Erythrovirus genus will constitute an important step towards proper diagnosis and management of infection. Immunodiagnostic methods have been used to test blood, serum, or plasma that is potentially contaminated with human erythrovirus. But such immunodiagnostic methods have limitations including, for example, inability to effectively detect recent or current infections and/or inability to distinguish between the different erythrovirus genotypes. There is still a need, therefore, for identifying and characterizing human erythrovirus variants and developing sensitive and effective assays for detecting them and/or distinguishing from among them.